Angular harmonic Hall voltage and magnetoresistance measurements of Pt/FeCoB and Pt-Ti/FeCoB bilayers for spin Hall conductivity determination

Abstract

Materials with significant spin-orbit coupling enable efficient spin-to-charge interconversion, which can be utilized in novel spin electronic devices. A number of elements, mainly heavy-metals (HM) have been identified to produce a sizable spin current ($j_{\mathrm{s}}$), while supplied with a charge current ($j$), detected mainly in the neighbouring ferromagnetic (FM) layer. Apart from the spin Hall angle ${\theta }_{\mathrm{SH}}$ = $j_{\mathrm{s}}$/$j$, spin Hall conductivity (${\sigma }_{\mathrm{SH}}$) is an important parameter, which takes also the resistivity of the material into account. In this work, we present a measurement protocol of the HM/FM bilayers, which enables for a precise ${\sigma }_{\mathrm{SH}}$ determination. Static transport measurements, including resistivity and magnetization measurements are accompanied by the angular harmonic Hall voltage analysis in a dedicated low-noise rotating probe station. Dynamic characterization includes effective magnetization and magnetization damping measurement, which enable HM/FM interface absorption calculation. We validate the measurement protocol in Pt and Pt-Ti underlayers in contact with FeCoB and present the ${\sigma }_{\mathrm{SH}}$ of up to 3.3$\times$10${}^5$ S/m, which exceeds the values typically measured in other HM, such as W or Ta.

7 pages, 5 figures, submitted to IEEE Transaction on Electron Devices

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